1. Technical Field
The present invention relates to an arrow signal recognition device that recognizes an arrow signal light provided to a traffic light, on the basis of an image captured by an onboard camera.
2. Related Art
Conventionally, a technique is known in which a traffic light and an arrow signal light provided to the traffic light are recognized based on a driving environment ahead of a vehicle that is image-captured by a camera (hereinafter referred to as “onboard camera”) mounted to the vehicle.
For example, Japanese Unexamined Patent Application Publication No. 2012-168592 discloses a technique of extracting an arrow signal light by detecting a red signal of a traffic light based on an image captured by an onboard camera and setting a search region for the arrow signal light based on the position of the red signal within the image to detect a pixel having a color feature amount of a predetermined RGB ratio within the set search region.
As traffic lights, there are light bulb traffic lights and LED traffic lights. Obviously, there are a light bulb type and an
LED type in arrow signal lights as well. In an LED arrow signal light, an arrow is formed by LEDs being arranged at predetermined intervals. Therefore, the luminance is approximately constant throughout. However, in a light bulb traffic light, the luminance gradually decreases away from a light bulb, since a cover lens is colored in the color of light with a blue filter or the like. Further, the brightness of the light bulb itself is not constant.
As a result, in the case where extraction of an arrow signal light is performed with a threshold being a color feature amount of a predetermined RGB ratio as disclosed in the document mentioned above, recognition itself of the arrow signal light may be difficult from afar where a vehicle equipped with this technique is relatively distant from a traffic light, for example. As a solution, it is conceivable to set a low color feature amount. However, there is a problem that the precision of recognition of an arrow signal light decreases.